Power Mac - MIA Hard Drive Space

I've got a G5 that had 130 GB of free space on it and last week I noticed it only had 82 GB free. There's nothing more ot less on it from previous weeks. Where did the space go? I also get the "running out of hard drive space, delete files" error message.

I have tried Disk Inventory X, Omni Disk Sweeper and Cache Out X. I can't find any large file that cold be hogging up the space. Can it be some invisible file or temp files?

I would consider investgating two locations. iMovie and iPhoto's Trash. Both apps have their own Trash and if not emptied once in a while, can become quite bloated. The reason they have their own Trash is that if you delete something but later want to reuse it - you can. You might edit a movie and trash the edits, then want that little bit of movie back again. The same goes for iPhoto.